Tanning is a very old art, which is a treatment for preventing the decomposition of raw hides or skins. The tanned raw hides, typically referred to as leather, are also flexible and very strong. Originally, tanning was accomplished by using vegetable tanning agents such as bark, leaf, or bean extracts. Bark extracts used include for example those that can be obtained from oak, hemlock or avaram trees. Leaf extracts used include those that can be obtained from for example sumac. Bean extracts can be obtained for example from the acacia tree.
Mineral tanning agents or tannins have gradually replaced vegetable tanning agents, because mineral tanning agents produce stronger and more flexible leathers from the raw skins. Of the mineral tannages, the most prominent used today is chromium sulfate. Zirconium and aluminum are other minerals widely used in tanning. Other natural tannages include aldehyde, which is toxic because it uses formaldehyde, and oil tannage. Oil tannage is primarily used for "chamois" leather. Syntans or synthetic organic tanning agents are also used. Of all these tannages, it is widely believed that "chrome" tannage produces the strongest leather.
For many years various attempts have been made to improve the function and appearance of leathers by changing the methods of tanning and by putting various additives into the tanning mixture during processing. When leather is used for various garments, such as for shoes and gloves, it is desirable that the leather have additional properties that would improve the comfort to the wearer and durability of the leather. For example, leathers have been stain-proofed and waterproofed using various additives. However, there remains a need for improved leather and improved processes for treating leather that provides a thermally enhanced leather, while maintaining the softness, stretchability, resilience, and appearance of the leather.